Biodegradable polylactic acid for use in nonwoven webs

ABSTRACT

A method for forming a biodegradable polylactic acid suitable for use in fibers is provided. In one embodiment, for example, a polylactic acid is melt blended with an alcohol to initiate an alcoholysis reaction that results in a polylactic acid having one or more hydroxyalkyl or alkyl terminal groups. By selectively controlling the alcoholysis conditions (e.g., alcohol and polymer concentrations, catalysts, temperature, etc.), a modified polylactic acid may be achieved that has a molecular weight lower than the starting polylactic acid. Such lower molecular weight polymers also have the combination of a higher melt flow index and lower apparent viscosity, which is useful in a wide variety of fiber forming applications, such as in the meltblowing of nonwoven webs.

BACKGROUND OF THE INVENTION

Biodegradable nonwoven webs are useful in a wide range of applications,such as in the formation of disposable absorbent products (e.g.,diapers, training pants, sanitary wipes, feminine pads and liners, adultincontinence pads, guards, garments, etc.). To facilitate formation ofthe nonwoven web, a biodegradable polymer should be selected that ismelt processable, yet also has good mechanical and physical properties.Polylactic acid (“PLA”) is one of the most common biodegradable andsustainable (renewable) polymers. Although various attempts have beenmade to use polylactic acid in the formation of nonwoven webs, its highmolecular weight and viscosity have generally restricted its use to onlycertain types of fiber forming processes. For example, conventionalpolylactic acids are not typically suitable for meltblowing processes,which require a low polymer viscosity for successful microfiberformation. As such, a need currently exists for a biodegradablepolylactic acid that exhibits good mechanical and physical properties,but which may be readily formed into a nonwoven web using a variety oftechniques (e.g., meltblowing).

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method forforming a biodegradable polymer for use in fiber formation is disclosed.The method comprises melt blending a first polylactic acid with at leastone alcohol so that the polylactic acid undergoes an alcoholysisreaction. The alcoholysis reaction results in a second, modifiedpolylactic acid having a melt flow index that is greater than the meltflow index of the first polylactic acid, determined at a load of 2160grams and temperature of 190° C. in accordance with ASTM Test MethodD1238-E.

In accordance with another embodiment of the present invention, a fiberis disclosed that comprises a biodegradable polylactic acid terminatedwith an alkyl group, hydroxyalkyl group, or a combination thereof. Thepolylactic acid has a melt flow index of from about 10 to about 1000grams per 10 minutes, determined at a load of 2160 grams and temperatureof 190° C. in accordance with ASTM Test Method D1238-E.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a schematic illustration of a process that may be used in oneembodiment of the present invention to form a nonwoven web;

FIG. 2 is a graph depicting apparent viscosity versus various shearrates for the extruded resins of Example 1;

FIG. 3 shows an SEM microphotograph (100×) of a meltblown web formed inExample 2;

FIG. 4 shows an SEM microphotograph (500×) of a meltblown web formed inExample 2;

FIG. 5 shows an SEM microphotograph (100×) of a thermally bondedmeltblown web formed in Example 2;

FIG. 6 shows an SEM microphotograph (500×) of a thermally bondedmeltblown web formed in Example 2; and

FIG. 7 shows an SEM microphotograph (1000×) of a thermally bondedmeltblown web formed in Example 2.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

Reference now will be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

DEFINITIONS

As used herein, the term “biodegradable” or “biodegradable polymer”generally refers to a material that degrades from the action ofnaturally occurring microorganisms, such as bacteria, fungi, and algae;environmental heat; moisture; or other environmental factors. Thebiodegradability of a material may be determined using ASTM Test Method5338.92.

As used herein, the term “fibers” refer to elongated extrudates formedby passing a polymer through a forming orifice such as a die. Unlessnoted otherwise, the term “fibers” includes discontinuous fibers havinga definite length and substantially continuous filaments. Substantiallyfilaments may, for instance, have a length much greater than theirdiameter, such as a length to diameter ratio (“aspect ratio”) greaterthan about 15,000 to 1, and in some cases, greater than about 50,000 to1.

As used herein, the term “monocomponent” refers to fibers formed onepolymer. Of course, this does not exclude fibers to which additives havebeen added for color, anti-static properties, lubrication,hydrophilicity, liquid repellency, etc.

As used herein, the term “multicomponent” refers to fibers formed fromat least two polymers (e.g., bicomponent fibers) that are extruded fromseparate extruders. The polymers are arranged in substantiallyconstantly positioned distinct zones across the cross-section of thefibers. The components may be arranged in any desired configuration,such as sheath-core, side-by-side, pie, island-in-the-sea, and so forth.Various methods for forming multicomponent fibers are described in U.S.Pat. No. 4,789,592 to Taniguchi et al. and U.S. Pat. Nos. 5,336,552 toStrack et al., 5,108,820 to Kaneko, et al., 4,795,668 to Kruege, et al.,5,382,400 to Pike, et al., 5,336,552 to Strack, et al., and 6,200,669 toMarmon, et al., which are incorporated herein in their entirety byreference thereto for all purposes. Multicomponent fibers having variousirregular shapes may also be formed, such as described in U.S. Pat. Nos.5,277,976 to Hogle, et al., 5,162,074 to Hills, 5,466,410 to Hills,5,069,970 to Largman, et al., and 5,057,368 to Largman, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes.

As used herein, the term “multiconstituent” refers to fibers formed fromat least two polymers (e.g., biconstituent fibers) that are extrudedfrom the same extruder. The polymers are not arranged in substantiallyconstantly positioned distinct zones across the cross-section of thefibers. Various multiconstituent fibers are described in U.S. Pat. No.5,108,827 to Gessner, which is incorporated herein in its entirety byreference thereto for all purposes.

As used herein, the term “nonwoven web” refers to a web having astructure of individual fibers that are randomly interlaid, not in anidentifiable manner as in a knitted fabric. Nonwoven webs include, forexample, meltblown webs, spunbond webs, carded webs, wet-laid webs,airlaid webs, coform webs, hydraulically entangled webs, etc. The basisweight of the nonwoven web may generally vary, but is typically fromabout 5 grams per square meter (“gsm”) to 200 gsm, in some embodimentsfrom about 10 gsm to about 150 gsm, and in some embodiments, from about15 gsm to about 100 gsm.

As used herein, the term “meltblown” web or layer generally refers to anonwoven web that is formed by a process in which a molten thermoplasticmaterial is extruded through a plurality of fine, usually circular, diecapillaries as molten fibers into converging high velocity gas (e.g.air) streams that attenuate the fibers of molten thermoplastic materialto reduce their diameter, which may be to microfiber diameter.Thereafter, the meltblown fibers are carried by the high velocity gasstream and are deposited on a collecting surface to form a web ofrandomly dispersed meltblown fibers. Such a process is disclosed, forexample, in U.S. Pat. Nos. 3,849,241 to Butin, et al.; 4,307,143 toMeitner, et al.; and 4,707,398 to Wisneski, et al., which areincorporated herein in their entirety by reference thereto for allpurposes. Meltblown fibers may be substantially continuous ordiscontinuous, and are generally tacky when deposited onto a collectingsurface.

As used herein, the term “spunbond” web or layer generally refers to anonwoven web containing small diameter substantially continuousfilaments. The filaments are formed by extruding a molten thermoplasticmaterial from a plurality of fine, usually circular, capillaries of aspinnerette with the diameter of the extruded filaments then beingrapidly reduced as by, for example, eductive drawing and/or otherwell-known spunbonding mechanisms. The production of spunbond webs isdescribed and illustrated, for example, in U.S. Pat. Nos. 4,340,563 toAppel, et al., 3,692,618 to Dorschner, et al., 3,802,817 to Matsuki, etal., 3,338,992 to Kinney, 3,341,394 to Kinney, 3,502,763 to Hartman,3,502,538 to Levy, 3,542,615 to Dobo, et al., and 5,382,400 to Pike, etal., which are incorporated herein in their entirety by referencethereto for all purposes. Spunbond filaments are generally not tackywhen they are deposited onto a collecting surface. Spunbond filamentsmay sometimes have diameters less than about 40 micrometers, and areoften between about 5 to about 20 micrometers.

As used herein, the term “carded web” refers to a web made from staplefibers that are sent through a combing or carding unit, which separatesor breaks apart and aligns the staple fibers in the machine direction toform a generally machine direction-oriented fibrous nonwoven web. Suchfibers are usually obtained in bales and placed in an opener/blender orpicker, which separates the fibers prior to the carding unit. Onceformed, the web may then be bonded by one or more known methods.

As used herein, the term “airlaid web” refers to a web made from bundlesof fibers having typical lengths ranging from about 3 to about 19millimeters (mm). The fibers are separated, entrained in an air supply,and then deposited onto a forming surface, usually with the assistanceof a vacuum supply. Once formed, the web is then bonded by one or moreknown methods.

As used herein, the term “coform web” generally refers to a compositematerial containing a mixture or stabilized matrix of thermoplasticfibers and a second non-thermoplastic material. As an example, coformmaterials may be made by a process in which at least one meltblown diehead is arranged near a chute through which other materials are added tothe web while it is forming. Such other materials may include, but arenot limited to, fibrous organic materials such as woody or non-woodypulp such as cotton, rayon, recycled paper, pulp fluff and alsosuperabsorbent particles, inorganic and/or organic absorbent materials,treated polymeric staple fibers and so forth. Some examples of suchcoform materials are disclosed in U.S. Pat. Nos. 4,100,324 to Anderson,et al.; 5,284,703 to Everhart, et al.; and 5,350,624 to Georger, et al.;which are incorporated herein in their entirety by reference thereto forall purposes.

DETAILED DESCRIPTION

The present invention is directed to a method for forming abiodegradable polylactic acid suitable for use in fibers. In oneembodiment, for example, a polylactic acid is melt blended with analcohol to initiate an alcoholysis reaction that results in a polylacticacid having one or more hydroxyalkyl or alkyl terminal groups. Byselectively controlling the alcoholysis conditions (e.g., alcohol andpolymer concentrations, catalysts, temperature, etc.), a modifiedpolylactic acid may be achieved that has a molecular weight lower thanthe starting polylactic acid. Such lower molecular weight polymers alsohave the combination of a higher melt flow index and lower apparentviscosity, which is useful in a wide variety of fiber formingapplications, such as in the meltblowing of nonwoven webs.

I. Reaction Components

A. Polylactic Acid

Polylactic acid may generally be derived from monomer units of anyisomer of lactic acid, such as levorotory-lactic acid (“L-lactic acid”),dextrorotatory-lactic acid (“D-lactic acid”), meso-lactic acid, ormixtures thereof. Monomer units may also formed from anhydrides of anyisomer of lactic acid, including L-lactide, D-lactide, meso-lactide, ormixtures thereof. Cyclic dimers of such lactic acids and/or lactides mayalso be employed. Any known polymerization method, such aspolycondensation or ring-opening polymerization, may be used topolymerize lactic acid. A small amount of a chain-extending agent (e.g.,a diisocyanate compound, an epoxy compound or an acid anhydride) mayalso be employed. The polylactic acid may be a homopolymer or acopolymer, such as one that contains monomer units derived from L-lacticacid and monomer units derived from D-lactic acid. Although notrequired, the rate of content of one of the monomer unit derived fromL-lactic acid and the monomer unit derived from D-lactic acid ispreferably about 85 mole % or more, in some embodiments about 90 mole %or more, and in some embodiments, about 95 mole % or more. Multiplepolylactic acids, each having a different ratio between the monomer unitderived from L-lactic acid and the monomer unit derived from D-lacticacid, may be blended at an arbitrary percentage.

In one particular embodiment, the polylactic acid has the followinggeneral structure:

One specific example of a suitable polylactic acid polymer that may beused in the present invention is commercially available from Biomer,Inc. of Krailling, Germany) under the name BIOMER™ L9000. Other suitablepolylactic acid polymers are commercially available from Natureworks,LLC of Minneapolis, Minn. (NATUREWORKS®) or Mitsui Chemical (LACEA™).Still other suitable polylactic acids may be described in U.S. Pat. Nos.4,797,468; 5,470,944; 5,770,682; 5,821,327; 5,880,254; and 6,326,458,which are incorporated herein in their entirety by reference thereto forall purposes.

The polylactic acid typically has a number average molecular weight(“M_(n)”) ranging from about 40,000 to about 160,000 grams per mole, insome embodiments from about 50,000 to about 140,000 grams per mole, andin some embodiments, from about 80,000 to about 120,000 grams per mole.Likewise, the polymer also typically has a weight average molecularweight (“M_(w)”) ranging from about 80,000 to about 200,000 grams permole, in some embodiments from about 100,000 to about 180,000 grams permole, and in some embodiments, from about 110,000 to about 160,000 gramsper mole. The ratio of the weight average molecular weight to the numberaverage molecular weight (“M_(w)/M_(n)”), i.e., the “polydispersityindex”, is also relatively low. For example, the polydispersity indextypically ranges from about 1.0 to about 3.0, in some embodiments fromabout 1.1 to about 2.0, and in some embodiments, from about 1.2 to about1.8. The weight and number average molecular weights may be determinedby methods known to those skilled in the art.

The polylactic acid may also have an apparent viscosity of from about 50to about 600 Pascal seconds (Pa·s), in some embodiments from about 100to about 500 Pa·s, and in some embodiments, from about 200 to about 400Pa·s, as determined at a temperature of 190° C. and a shear rate of 1000sec⁻¹. The melt flow index of the polylactic acid may also range fromabout 0.1 to about 40 grams per 10 minutes, in some embodiments fromabout 0.5 to about 20 grams per 10 minutes, and in some embodiments,from about 5 to about 15 grams per 10 minutes. The melt flow index isthe weight of a polymer (in grams) that may be forced through anextrusion rheometer orifice (0.0825-inch diameter) when subjected to aload of 2160 grams in 10 minutes at a certain temperature (e.g., 190°C.), measured in accordance with ASTM Test Method D1238-E.

The polylactic acid also typically has a melting point of from about100° C. to about 240° C., in some embodiments from about 120° C. toabout 220° C., and in some embodiments, from about 140° C. to about 200°C. Such low melting point polylactic acids are useful in that theybiodegrade at a fast rate and are generally soft. The glass transitiontemperature (“T_(g)”) of the polylactic acid is also relatively low toimprove flexibility and processability of the polymers. For example, theT_(g) may be about 80° C. or less, in some embodiments about 70° C. orless, and in some embodiments, about 65° C. or less. As discussed inmore detail below, the melting temperature and glass transitiontemperature may all be determined using differential scanningcalorimetry (“DSC”) in accordance with ASTM D-3417.

B. Alcohol

As indicated above, the polylactic acid may be reacted with an alcoholto form a modified polylactic acid having a reduced molecular weight.The concentration of the alcohol reactant may influence the extent towhich the molecular weight is altered. For instance, higher alcoholconcentrations generally result in a more significant decrease inmolecular weight. Of course, too high of an alcohol concentration mayalso affect the physical characteristics of the resulting polymer. Thus,in most embodiments, the alcohol(s) are employed in an amount of about0.1 wt. % to about 20 wt. %, in some embodiments from about 0.2 wt. % toabout 10 wt. %, and in some embodiments, from about 0.5 wt. % to about 5wt. %, based on the total weight of the starting polylactic acid.

The alcohol may be monohydric or polyhydric (dihydric, trihydric,tetrahydric, etc.), saturated or unsaturated, and optionally substitutedwith functional groups, such as carboxyl, amine, etc. Examples ofsuitable monohydric alcohols include methanol, ethanol, 1-propanol,2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,1-hexanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol,4-heptanol, 1-octanol, 2-octanol, 3-octanol, 4-octanol, 1-nonanol,2-nonanol, 3-nonanol, 4-nonanol, 5-nonanol, 1-decanol, 2-decanol,3-decanol, 4-decanol, 5-decanol, allyl alcohol, 1-butenol, 2-butenol,1-pentenol, 2-pentenol, 1-hexenol, 2-hexenol, 3-hexenol, 1-heptenol,2-heptenol, 3-heptenol, 1-octenol, 2-octenol, 3-octenol, 4-octenol,1-nonenol, 2-nonenol, 3-nonenol, 4-nonenol, 1-decenol, 2-decenol,3-decenol, 4-decenol, 5-decenol, cyclohexanol, cyclopentanol,cycloheptanol, 1-phenythyl alcohol, 2-phenythyl alcohol,2-ethoxy-ethanol, methanolamine, ethanolamine, and so forth. Examples ofsuitable dihydric alcohols include 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1-hydroxymethyl-2-hydroxyethylcyclohexane,1-hydroxy-2-hydroxypropylcyclohexane,1-hydroxy-2-hydroxyethylcyclohexane,1-hydroxymethyl-2-hydroxyethylbenzene,1-hydroxymethyl-2-hydroxypropylbenzene, 1-hydroxy-2-hydroxyethylbenzene,1,2-benzylmethylol, 1,3-benzyldimethylol, and so forth. Suitabletrihydric alcohols may include glycerol, trimethylolpropane, etc., whilesuitable tetrahydric alcohols may include pentaerythritol, erythritol,etc. Preferred alcohols are dihydric alcohols having from 2 to 6 carbonatoms, such as 1,3-propanediol and 1,4-butanediol.

The hydroxy group of the alcohol is generally capable of attacking anester linkage of the starting polylactic acid, thereby leading to chainscission or “depolymerization” of the polylactic acid molecule into oneor more shorter ester chains. The shorter chains may include polylacticacids, as well as minor portions of lactic acid monomers or oligomers,and combinations of any of the foregoing. Although not necessarilyrequired, the short chain polylactic acids formed during alcoholysis areoften terminated with an alkyl and/or hydroxyalkyl groups derived fromthe alcohol. Alkyl group terminations are typically derived frommonohydric alcohols, while hydroxyalkyl group terminations are typicallyderived from polyhydric alcohols. In one particular embodiment, forexample, a polylactic acid is formed during the alcoholysis reactionhaving the following general structure:

wherein,

y is an integer greater than 1; and

R₁ and R₂ are independently selected from hydrogen; hydroxyl groups;straight chain or branched, substituted or unsubstituted C₁-C₁₀ alkylgroups; straight chain or branched, substituted or unsubstituted C₁-C₁₀hydroxalkyl groups. Preferably, at least one of R₁ and R₂, or both, arestraight chain or branched, substituted or unsubstituted, C₁-C₁₀ alkylor C₁-C₁₀ hydroxyalkyl groups, in some embodiments C₁-C₈ alkyl or C₁-C₈hydroxyalkyl groups, and in some embodiments, C₂-C₆ alkyl or C₂-C₆hydroxyalkyl groups. Examples of suitable alkyl and hydroxyalkyl groupsinclude, for instance, methyl, ethyl, iso-propyl, n-propyl, n-butyl,isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl,n-decyl, 1-hydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl,4-hydroxybutyl, and 5-hydroxypentyl groups. Thus, as indicated, themodified polylactic acid has a different chemical composition than anunmodified polylactic acid in terms of its terminal groups. The terminalgroups may play a substantial role in determining the properties of thepolymer, such as its reactivity, stability, etc.

Regardless of its particular structure, a new polymer species is formedduring alcoholysis that has a molecular weight lower than that of thestarting polylactic acid. The weight average and/or number averagemolecular weights may, for instance, each be reduced so that the ratioof the starting polylactic acid molecular weight to the modifiedpolylactic acid molecular weight is at least about 1.1, in someembodiments at least about 1.4, and in some embodiments, at least about2.0. For example, the modified polylactic acid may have a number averagemolecular weight (“M_(n)”) ranging from about 10,000 to about 105,000grams per mole, in some embodiments from about 20,000 to about 100,000grams per mole, and in some embodiments, from about 30,000 to about90,000 grams per mole. Likewise, the modified polylactic acid may alsohave a weight average molecular weight (“M_(w)”) of from about 20,000 toabout 140,000 grams per mole, in some embodiments from about 30,000 toabout 120,000 grams per mole, and in some embodiments, from about 50,000to about 100,000 grams per mole.

In addition to possessing a lower molecular weight, the modifiedpolylactic acid may also have a lower apparent viscosity and higher meltflow index than the starting polymer. The apparent viscosity may forinstance, be reduced so that the ratio of the starting polylactic acidviscosity to the modified polylactic acid viscosity is at least about1.1, in some embodiments at least about 2, and in some embodiments, fromabout 15 to about 50. Likewise, the melt flow index may be increased sothat the ratio of the modified polylactic acid melt flow index to thestarting polylactic acid melt flow index is at least about 1.5, in someembodiments at least about 5, in some embodiments at least about 10, andin some embodiments, from about 30 to about 100. In one particularembodiment, the modified polylactic acid may have an apparent viscosityof from about 5 to about 250 Pascal seconds (Pa·s), in some embodimentsfrom about 8 to about 150 Pa·s, and in some embodiments, from about 10to about 100 Pa·s, as determined at a temperature of 190° C. and a shearrate of 1000 sec⁻¹. The melt flow index of the modified polylactic acidmay range from about 10 to about 1000 grams per 10 minutes, in someembodiments from about 20 to about 900 grams per 10 minutes, and in someembodiments, from about 100 to about 800 grams per 10 minutes (190° C.,2.16 kg). Of course, the extent to which the molecular weight, apparentviscosity, and/or melt flow index are altered by the alcoholysisreaction may vary depending on the intended application.

Although differing from the starting polymer in certain properties, themodified polylactic acid may nevertheless retain other properties of thestarting polymer to enhance the flexibility and processability of thepolymers. For example, the thermal characteristics (e.g., T_(g), T_(m),and latent heat of fusion) typically remain substantially the same asthe starting polymer, such as within the ranges noted above. Further,even though the actual molecular weights may differ, the polydispersityindex of the modified polylactic acid may remain substantially the sameas the starting polymer, such as within the range of about 1.0 to about3.0, in some embodiments from about 1.1 to about 2.0, and in someembodiments, from about 1.2 to about 1.8.

C. Catalyst

A catalyst may be employed to facilitate the modification of thealcoholysis reaction. The concentration of the catalyst may influencethe extent to which the molecular weight is altered. For instance,higher catalyst concentrations generally result in a more significantdecrease in molecular weight. Of course, too high of a catalystconcentration may also affect the physical characteristics of theresulting polymer. Thus, in most embodiments, the catalyst(s) areemployed in an amount of about 50 to about 2000 parts per million(“ppm”), in some embodiments from about 100 to about 1000 ppm, and insome embodiments, from about 200 to about 1000 ppm, based on the weightof the starting polylactic acid.

Any known catalyst may be used in the present invention to accomplishthe desired reaction. In one embodiment, for example, a transition metalcatalyst may be employed, such as those based on Group IVB metals and/orGroup IVA metals (e.g., alkoxides or salts). Titanium-, zirconium-,and/or tin-based metal catalysts are especially desirable and mayinclude, for instance, titanium butoxide, titanium tetrabutoxide,titanium propoxide, titanium isopropoxide, titanium phenoxide, zirconiumbutoxide, dibutyltin oxide, dibutyltin diacetate, tin phenoxide, tinoctylate, tin stearate, dibutyltin dioctoate, dibutyltin dioleylmaleate,dibutyltin dibutylmaleate, dibutyltin dilaurate,1,1,3,3-tetrabutyl-1,3-dilauryloxycarbonyldistannoxane,dibutyltindiacetate, dibutyltin diacetylacetonate, dibutyltinbis(o-phenylphenoxide), dibutyltin bis(triethoxysilicate), dibutyltindistearate, dibutyltin bis(isononyl-3-mercaptopropionate), dibutyltinbis(isooctyl thioglycolate), dioctyltin oxide, dioctyltin dilaurate,dioctyltin diacetate, and dioctyltin diversatate.

D. Co-Solvent

The alcoholysis reaction is typically carried out in the absence of asolvent other than the alcohol reactant. Nevertheless, a co-solvent maybe employed in some embodiments of the present invention. In oneembodiment, for instance, the co-solvent may facilitate the dispersionof the catalyst in the reactant alcohol. Examples of suitableco-solvents may include ethers, such as diethyl ether, anisole,tetrahydrofuran, ethylene glycol dimethyl ether, triethylene glycoldimethyl ether, tertraethylene glycol dimethyl ether, dioxane, etc.;alcohols, such as methanol, ethanol, n-butanol, benzyl alcohol, ethyleneglycol, diethylene glycol, etc.; phenols, such as phenol, etc.;carboxylic acids, such as formic acid, acetic acid, propionic acid,toluic acid, etc.; esters, such as methyl acetate, butyl acetate, benzylbenzoate, etc.; aromatic hydrocarbons, such as benzene, toluene,ethylbenzene, tetralin, etc.; aliphatic hydrocarbons, such as n-hexane,n-octane, cyclohexane, etc.; halogenated hydrocarbons, such asdichloromethane, trichloroethane, chlorobenzene, etc.; nitro compounds,such as nitromethane, nitrobenzene, etc.; carbamides, such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.;ureas, such as N,N-dimethylimidazolidinone, etc.; sulfones, such asdimethyl sulfone, etc.; sulfoxides, such as dimethyl sulfoxide, etc.;lactones, such as butyrolactone, caprolactone, etc.; carbonic acidesters, such as dimethyl carbonate, ethylene carbonate, etc.; and soforth.

When employed, the co-solvent(s) may be employed in an amount from about0.5 wt. % to about 20 wt. %, in some embodiments from about 0.8 wt. % toabout 10 wt. %, and in some embodiments, from about 1 wt. % to about 5wt. %, based on the weight of the reactive composition. It should beunderstood, however, that a co-solvent is not required. In fact, in someembodiments of the present invention, the reactive composition issubstantially free of any co-solvents, e.g., less than about 0.5 wt. %of the reactive composition.

E. Other Ingredients

Other ingredients may of course be utilized for a variety of differentreasons. For instance, a wetting agent may be employed in someembodiments of the present invention to improve hydrophilicity. Wettingagents suitable for use in the present invention are generallycompatible with polylactic acids. Examples of suitable wetting agentsmay include surfactants, such as UNITHOX® 480 and UNITHOX® 750ethoxylated alcohols, or UNICID™ acid amide ethoxylates, all availablefrom Petrolite Corporation of Tulsa, Okla. Other suitable wetting agentsare described in U.S. Pat. No. 6,177,193 to Tsai, et al., which isincorporated herein in its entirety by reference thereto for allrelevant purposes. Still other materials that may be used include,without limitation, melt stabilizers, processing stabilizers, heatstabilizers, light stabilizers, antioxidants, pigments, surfactants,waxes, flow promoters, plasticizers, particulates, and other materialsadded to enhance processability. When utilized, such additionalingredients are each typically present in an amount of less than about 5wt. %, in some embodiments less than about 1 wt. %, and in someembodiments, less than about 0.5 wt. %, based on the weight of thestarting polylactic acid.

II. Reaction Technique

The alcoholysis reaction may be performed using any of a variety ofknown techniques. In one embodiment, for example, the reaction isconducted while the starting polymer is in the melt phase (“meltblending”) to minimize the need for additional solvents and/or solventremoval processes. The raw materials (e.g., biodegradable polymer,alcohol, catalyst, etc.) may be supplied separately or in combination(e.g., in a solution). The raw materials may likewise be supplied eithersimultaneously or in sequence to a melt-blending device thatdispersively blends the materials. Batch and/or continuous melt blendingtechniques may be employed. For example, a mixer/kneader, Banbury mixer,Farrel continuous mixer, single-screw extruder, twin-screw extruder,roll mill, etc., may be utilized to blend the materials. Oneparticularly suitable melt-blending device is a co-rotating, twin-screwextruder (e.g., ZSK-30 twin-screw extruder available from Werner &Pfleiderer Corporation of Ramsey, N.J.). Such extruders may includefeeding and venting ports and provide high intensity distributive anddispersive mixing, which facilitate the alcoholysis reaction. Forexample, the polylactic acid may be fed to a feeding port of thetwin-screw extruder and melted. Thereafter, the alcohol may be injectedinto the polymer melt. Alternatively, the alcohol may be separately fedinto the extruder at a different point along its length. The catalyst, amixture of two or more catalysts, or catalyst solutions may be injectedseparately or in combination with the alcohol or a mixture of two ormore alcohols to the polymer melt.

Regardless of the particular melt blending technique chosen, the rawmaterials are blended under high shear/pressure and heat to ensuresufficient mixing for initiating the alcoholysis reaction. For example,melt blending may occur at a temperature of from about 60° C. to about300° C., in some embodiments, from about 100° C. to about 250° C., andin some embodiments, from about 150° C. to about 220° C. Likewise, theapparent shear rate during melt blending may range from about 100seconds⁻¹ to about 10,000 seconds⁻¹, in some embodiments from about 500seconds⁻¹ to about 5000 seconds⁻¹, and in some embodiments, from about800 seconds⁻¹ to about 1200 seconds⁻¹. The apparent shear rate is equalto 4Q/πR³, where Q is the volumetric flow rate (“m³/s”) of the polymermelt and R is the radius (“m”) of the capillary (e.g., extruder die)through which the melted polymer flows.

III. Fiber Formation

Fibers formed from the modified polylactic acid may generally have anydesired configuration, including monocomponent, multicomponent (e.g.,sheath-core configuration, side-by-side configuration, pieconfiguration, island-in-the-sea configuration, and so forth), and/ormulticonstituent. In some embodiments, the fibers may contain one ormore strength-enhancing polymers as a component (e.g., bicomponent) orconstituent (e.g., biconstituent) to further enhance strength and othermechanical properties. The strength-enhancing polymer may be athermoplastic polymer that is not generally considered biodegradable,such as polyolefins, e.g., polyethylene, polypropylene, polybutylene,and so forth; polytetrafluoroethylene; polyvinyl acetate; polyvinylchloride acetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate,polymethylacrylate, polymethylmethacrylate, and so forth; polyamides,e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene;polyvinyl alcohol; and polyurethanes. More desirably, however, thestrength-enhancing polymer is biodegradable, such as aliphaticpolyesters, aromatic polyesters; aliphatic-aromatic polyesters; andblends thereof.

Any of a variety of processes may be used to form fibers in accordancewith the present invention. Referring to FIG. 1, for example, oneembodiment of a method for forming meltblown fibers is shown. Meltblownfibers form a structure having a small average pore size, which may beused to inhibit the passage of liquids and particles, while allowinggases (e.g., air and water vapor) to pass therethrough. To achieve thedesired pore size, the meltblown fibers are typically “microfibers” inthat they have an average size of 10 micrometers or less, in someembodiments about 7 micrometers or less, and in some embodiments, about5 micrometers or less. The ability to produce such fine fibers may befacilitated in the present invention through the use of a modifiedpolylactic acid having the desirable combination of low apparentviscosity and high melt flow index.

In FIG. 1, for instance, the raw materials (e.g., polymer, alcohol,catalyst, etc.) are fed into an extruder 12 from a hopper 10. The rawmaterials may be provided to the hopper 10 using any conventionaltechnique and in any state. For example, the alcohol may be supplied asa vapor or liquid. Alternatively, the polylactic acid may be fed to thehopper 10, and the alcohol and optional catalyst (either in combinationor separately) may be injected into the polymer melt in the extruder 12downstream from the hopper 10. The extruder 12 is driven by a motor 11and heated to a temperature sufficient to extrude the polymer and toinitiate the alcoholysis reaction. For example, the extruder 12 mayemploy one or multiple zones operating at a temperature of from about60° C. to about 300° C., in some embodiments, from about 100° C. toabout 250° C., and in some embodiments, from about 150° C. to about 220°C. Typical shear rates range from about 100 seconds⁻¹ to about 10,000seconds⁻¹, in some embodiments from about 500 seconds⁻¹ to about 5000seconds⁻¹, and in some embodiments, from about 800 seconds-1 to about1200 seconds⁻¹.

Once formed, the modified polylactic acid may be subsequently fed toanother extruder in a fiber formation line (e.g., extruder 12 of ameltblown spinning line). Alternatively, the modified polylactic acidmay be directly formed into a fiber through supply to a die 14, whichmay be heated by a heater 16. It should be understood that othermeltblown die tips may also be employed. As the polymer exits the die 14at an orifice 19, high pressure fluid (e.g., heated air) supplied byconduits 13 attenuates and spreads the polymer stream into microfibers18. Although not shown in FIG. 1, the die 14 may also be arrangedadjacent to or near a chute through which other materials (e.g.,cellulosic fibers, particles, etc.) traverse to intermix with theextruded polymer and form a “coform” web.

The microfibers 18 are randomly deposited onto a foraminous surface 20(driven by rolls 21 and 23) with the aid of an optional suction box 15to form a meltblown web 22. The distance between the die tip and theforaminous surface 20 is generally small to improve the uniformity ofthe fiber laydown. For example, the distance may be from about 1 toabout 35 centimeters, and in some embodiments, from about 2.5 to about15 centimeters. In FIG. 1, the direction of the arrow 28 shows thedirection in which the web is formed (i.e., “machine direction”) andarrow 30 shows a direction perpendicular to the machine direction (i.e.,“cross-machine direction”). Optionally, the meltblown web 22 may then becompressed by rolls 24 and 26. The desired denier of the fibers may varydepending on the desired application. Typically, the fibers are formedto have a denier per filament of less than about 6, in some embodimentsless than about 3, and in some embodiments, from about 0.5 to about 3.In addition, the fibers generally have an average diameter of from about0.1 to about 20 micrometers, in some embodiments from about 0.5 to about15 micrometers, and in some embodiments, from about 1 to about 10micrometers.

Once formed, the nonwoven web may then be bonded using any conventionaltechnique, such as with an adhesive or autogenously (e.g., fusion and/orself-adhesion of the fibers without an applied external adhesive).Autogenous bonding, for instance, may be achieved through contact of thefibers while they are semi-molten or tacky, or simply by blending atackifying resin and/or solvent with the polylactic acid(s) used to formthe fibers. Suitable autogenous bonding techniques may includeultrasonic bonding, thermal bonding, through-air bonding, and so forth.

For instance, the web may be passed through a nip formed between a pairof rolls, one or both of which are heated to melt-fuse the fibers. Oneor both of the rolls may also contain intermittently raised bond pointsto provide an intermittent bonding pattern. The pattern of the raisedpoints is generally selected so that the nonwoven web has a total bondarea of less than about 50% (as determined by conventional opticalmicroscopic methods), and in some embodiments, less than about 30%.Likewise, the bond density is also typically greater than about 100bonds per square inch, and in some embodiments, from about 250 to about500 pin bonds per square inch. Such a combination of total bond area andbond density may be achieved by bonding the web with a pin bond patternhaving more than about 100 pin bonds per square inch that provides atotal bond surface area less than about 30% when fully contacting asmooth anvil roll. In some embodiments, the bond pattern may have a pinbond density from about 250 to about 350 pin bonds per square inch and atotal bond surface area from about 10% to about 25% when contacting asmooth anvil roll. Exemplary bond patterns include, for instance, thosedescribed in U.S. Pat. No. 3,855,046 to Hansen et al., U.S. Pat. No.5,620,779 to Levy et al., U.S. Pat. No. 5,962,112 to Haynes et al., U.S.Pat. No. 6,093,665 to Sayovitz et al., U.S. Design Pat. No. 428,267 toRomano et al. and U.S. Design Pat. No. 390,708 to Brown, which areincorporated herein in their entirety by reference thereto for allpurposes.

Due to the particular rheological and thermal properties of the modifiedpolylactic acid used to form the fibers, the web bonding conditions(e.g., temperature and nip pressure) may be selected to cause thepolymer to melt and flow at relatively low temperatures. For example,the bonding temperature (e.g., the temperature of the rollers) may befrom about 50° C. to about 160° C., in some embodiments from about 60°C. to about 160° C., and in some embodiments, from about 80° C. to about140° C. Likewise, the nip pressure may range from about 5 to about 150pounds per square inch, in some embodiments, from about 10 to about 100pounds per square inch, and in some embodiments, from about 30 to about60 pounds per square inch.

In addition to meltblown webs, a variety of other nonwoven webs may alsobe formed from the modified polylactic acid in accordance with thepresent invention, such as spunbond webs, bonded carded webs, wet-laidwebs, airlaid webs, coform webs, hydraulically entangled webs, etc. Forexample, the polymer may be extruded through a spinnerette, quenched anddrawn into substantially continuous filaments, and randomly depositedonto a forming surface. Alternatively, the polymer may be formed into acarded web by placing bales of fibers formed from the blend into apicker that separates the fibers. Next, the fibers are sent through acombing or carding unit that further breaks apart and aligns the fibersin the machine direction so as to form a machine direction-orientedfibrous nonwoven web. Once formed, the nonwoven web is typicallystabilized by one or more known bonding techniques.

The fibers of the present invention may constitute the entire fibrouscomponent of the nonwoven web or blended with other types of fibers(e.g., staple fibers, filaments, etc). When blended with other types offibers, it is normally desired that the fibers of the present inventionconstitute from about 20 wt % to about 95 wt. %, in some embodimentsfrom about 30 wt. % to about 90 wt. %, and in some embodiments, fromabout 40 wt. % to about 80 wt. % of the total amount of fibers employedin the nonwoven web. For example, additional monocomponent and/ormulticomponent synthetic fibers may be utilized in the nonwoven web.Some suitable polymers that may be used to form the synthetic fibersinclude, but are not limited to: polyolefins, e.g., polyethylene,polypropylene, polybutylene, and so forth; polytetrafluoroethylene;polylactic acids, e.g., polyethylene terephthalate and so forth;polyvinyl acetate; polyvinyl chloride acetate; polyvinyl butyral;acrylic resins, e.g., polyacrylate, polymethylacrylate,polymethylmethacrylate, and so forth; polyamides, e.g., nylon; polyvinylchloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol;polyurethanes; polylactic acid; etc. If desired, biodegradable polymers,such as poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(β-malicacid) (PMLA), poly(ε-caprolactone) (PCL), poly(ρ-dioxanone) (PDS),poly(butylene succinate) (PBS), and poly(3-hydroxybutyrate) (PHB), mayalso be employed. Some examples of known synthetic fibers includesheath-core bicomponent fibers available from KoSa Inc. of Charlotte,N.C. under the designations T-255 and T-256, both of which use apolyolefin sheath, or T-254, which has a low melt co-polylactic acidsheath. Still other known bicomponent fibers that may be used includethose available from the Chisso Corporation of Moriyama, Japan orFibervisions LLC of Wilmington, Del. Synthetic or natural cellulosicpolymers may also be used, including but not limited to, cellulosicesters; cellulosic ethers; cellulosic nitrates; cellulosic acetates;cellulosic acetate butyrates; ethyl cellulose; regenerated celluloses,such as viscose, rayon, and so forth.

The fibers of the present invention may also be blended with pulpfibers, such as high-average fiber length pulp, low-average fiber lengthpulp, or mixtures thereof. One example of suitable high-average lengthfluff pulp fibers includes softwood kraft pulp fibers. Softwood kraftpulp fibers are derived from coniferous trees and include pulp fiberssuch as, but not limited to, northern, western, and southern softwoodspecies, including redwood, red cedar, hemlock, Douglas fir, true firs,pine (e.g., southern pines), spruce (e.g., black spruce), combinationsthereof, and so forth. Northern softwood kraft pulp fibers may be usedin the present invention. An example of commercially available southernsoftwood kraft pulp fibers suitable for use in the present inventioninclude those available from Weyerhaeuser Company with offices inFederal Way, Wash. under the trade designation of “NB-416.” Anothersuitable pulp for use in the present invention is a bleached, sulfatewood pulp containing primarily softwood fibers that is available fromBowater Corp. with offices in Greenville, S.C. under the trade nameCoosAbsorb S pulp. Low-average length fibers may also be used in thepresent invention. An example of suitable low-average length pulp fibersis hardwood kraft pulp fibers. Hardwood kraft pulp fibers are derivedfrom deciduous trees and include pulp fibers such as, but not limitedto, eucalyptus, maple, birch, aspen, etc. Eucalyptus kraft pulp fibersmay be particularly desired to increase softness, enhance brightness,increase opacity, and change the pore structure of the sheet to increaseits wicking ability.

Nonwoven laminates may also be formed in which one or more layers areformed from the modified polylactic acid of the present invention. Inone embodiment, for example, the nonwoven laminate contains a meltblownlayer positioned between two spunbond layers to form aspunbond/meltblown/spunbond (“SMS”) laminate. If desired, the meltblownlayer may be formed from the modified polylactic acid. The spunbondlayer may be formed from the modified polylactic acid, otherbiodegradable polymer(s), and/or any other polymer (e.g., polyolefins).Various techniques for forming SMS laminates are described in U.S. Pat.Nos. 4,041,203 to Brock et al.; 5,213,881 to Timmons, et al.; 5,464,688to Timmons, et al.; 4,374,888 to Bornslaeger; 5,169,706 to Collier, etal.; and 4,766,029 to Brock et al., as well as U.S. Patent ApplicationPublication No. 2004/0002273 to Fitting, et al., all of which areincorporated herein in their entirety by reference thereto for allpurposes. Of course, the nonwoven laminate may have other configurationand possess any desired number of meltblown and spunbond layers, such asspunbond/meltblown/meltblown/spunbond laminates (“SMMS”),spunbond/meltblown laminates (“SM”), etc. Although the basis weight ofthe nonwoven laminate may be tailored to the desired application, itgenerally ranges from about 10 to about 300 grams per square meter(“gsm”), in some embodiments from about 25 to about 200 gsm, and in someembodiments, from about 40 to about 150 gsm.

If desired, the nonwoven web or laminate may be applied with varioustreatments to impart desirable characteristics. For example, the web maybe treated with liquid-repellency additives, antistatic agents,surfactants, colorants, antifogging agents, fluorochemical blood oralcohol repellents, lubricants, and/or antimicrobial agents. Inaddition, the web may be subjected to an electret treatment that impartsan electrostatic charge to improve filtration efficiency. The charge mayinclude layers of positive or negative charges trapped at or near thesurface of the polymer, or charge clouds stored in the bulk of thepolymer. The charge may also include polarization charges that arefrozen in alignment of the dipoles of the molecules. Techniques forsubjecting a fabric to an electret treatment are well known by thoseskilled in the art. Examples of such techniques include, but are notlimited to, thermal, liquid-contact, electron beam and corona dischargetechniques. In one particular embodiment, the electret treatment is acorona discharge technique, which involves subjecting the laminate to apair of electrical fields that have opposite polarities. Other methodsfor forming an electret material are described in U.S. Pat. Nos.4,215,682 to Kubik. et al.; 4,375,718 to Wadsworth; 4,592,815 to Nakao;4,874,659 to Ando; 5,401,446 to Tsai, et al.; 5,883,026 to Reader, etal.; 5,908,598 to Rousseau, et al.; 6,365,088 to Knight, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes.

The nonwoven web or laminate may be used in a wide variety ofapplications. For example, the web may be incorporated into a “medicalproduct”, such as gowns, surgical drapes, facemasks, head coverings,surgical caps, shoe coverings, sterilization wraps, warming blankets,heating pads, and so forth. Of course, the nonwoven web may also be usedin various other articles. For example, the nonwoven web may beincorporated into an “absorbent article” that is capable of absorbingwater or other fluids. Examples of some absorbent articles include, butare not limited to, personal care absorbent articles, such as diapers,training pants, absorbent underpants, incontinence articles, femininehygiene products (e.g., sanitary napkins), swim wear, baby wipes, mittwipe, and so forth; medical absorbent articles, such as garments,fenestration materials, underpads, bedpads, bandages, absorbent drapes,and medical wipes; food service wipers; clothing articles; pouches, andso forth. Materials and processes suitable for forming such articles arewell known to those skilled in the art. Absorbent articles, forinstance, typically include a substantially liquid-impermeable layer(e.g., outer cover), a liquid-permeable layer (e.g., bodyside liner,surge layer, etc.), and an absorbent core. In one embodiment, forexample, the nonwoven web of the present invention may be used to forman outer cover of an absorbent article.

The present invention may be better understood with reference to thefollowing examples.

Test Methods

Molecular Weight:

The molecular weight distribution of a polymer was determined by gelpermeation chromatography (“GPC”). The samples were initially preparedby adding 0.5% wt/v solutions of the sample polymers in chloroform to40-milliliter glass vials. For example, 0.05±0.0005 grams of the polymerwas added to 10 milliliters of chloroform. The prepared samples wereplaced on an orbital shaker and agitated overnight. The dissolved samplewas filtered through a 0.45-micrometer PTFE membrane and analyzed usingthe following conditions:

-   Columns: Styragel HR 1, 2, 3, 4, & 5E (5 in series) at 41° C.-   Solvent/Eluent: Chloroform @1.0 milliliter per minute-   HPLC: Waters 600E gradient pump and controller, Waters 717 auto    sampler-   Detector: Waters 2414 Differential Refractometer at sensitivity=30,    at 40° C. and scale factor of 20-   Sample Concentration: 0.5% of polymer “as is”-   Injection Volume: 50 microliters-   Calibration Standards: Narrow MW polystyrene, 30-microliter injected    volume.

Number Average Molecular Weight (MW_(n)), Weight Average MolecularWeight (MW_(w)) and first moment of viscosity average molecular weight(MW_(z)) were obtained.

Apparent Viscosity:

The rheological properties of polymer samples were determined using aGötifert Rheograph 2003 capillary rheometer with WinRHEO version 2.31analysis software. The setup included a 2000-bar pressure transducer anda 30/1:0/180 roundhole capillary die. Sample loading was done byalternating between sample addition and packing with a ramrod. A2-minute melt time preceded each test to allow the polymer to completelymelt at the test temperature (usually 150° C. to 220° C.). The capillaryrheometer determined the apparent viscosity (Pa·s) at various shearrates, such as 100, 200, 500, 1000, 2000, and 4000 s⁻¹. The resultantrheology curve of apparent shear rate versus apparent viscosity gave anindication of how the polymer would run at that temperature in anextrusion process.

Melt Flow Index:

The melt flow index is the weight of a polymer (in grams) forced throughan extrusion rheometer orifice (0.0825-inch diameter) when subjected toa load of 2160 grams in 10 minutes (usually 150° C. to 230° C.). Unlessotherwise indicated, the melt flow index was measured in accordance withASTM Test Method D1238-E.

Thermal Properties:

The melting temperature (“T_(m)”), glass transition temperature(“T_(g)”), and latent heat of fusion (“ΔH_(f)”) were determined bydifferential scanning calorimetry (DSC). The differential scanningcalorimeter was a THERMAL ANALYST 2910 Differential ScanningCalorimeter, which was outfitted with a liquid nitrogen coolingaccessory and with a THERMAL ANALYST 2200 (version 8.10) analysissoftware program, both of which are available from T.A. Instruments Inc.of New Castle, Del. To avoid directly handling the samples, tweezers orother tools were used. The samples were placed into an aluminum pan andweighed to an accuracy of 0.01 milligram on an analytical balance. A lidwas crimped over the material sample onto the pan. Typically, the resinpellets were placed directly in the weighing pan, and the fibers werecut to accommodate placement on the weighing pan and covering by thelid.

The differential scanning calorimeter was calibrated using an indiummetal standard and a baseline correction was performed, as described inthe operating manual for the differential scanning calorimeter. Amaterial sample was placed into the test chamber of the differentialscanning calorimeter for testing, and an empty pan is used as areference. All testing was run with a 55-cubic centimeter per minutenitrogen (industrial grade) purge on the test chamber. For resin pelletsamples, the heating and cooling program was a 2-cycle test that beganwith an equilibration of the chamber to −25° C., followed by a firstheating period at a heating rate of 10° C. per minute to a temperatureof 200° C., followed by equilibration of the sample at 200° C. for 3minutes, followed by a first cooling period at a cooling rate of 20° C.per minute to a temperature of −25° C., followed by equilibration of thesample at −25° C. for 3 minutes, and then a second heating period at aheating rate of 10° C. per minute to a temperature of 200° C. For fibersamples, the heating and cooling program was a 1-cycle test that beganwith an equilibration of the chamber to −25° C., followed by a heatingperiod at a heating rate of 20° C. per minute to a temperature of 200°C., followed by equilibration of the sample at 200° C. for 3 minutes,and then a cooling period at a cooling rate of 1° C. per minute to atemperature of −25° C. All testing was run with a 55-cubic centimeterper minute nitrogen (industrial grade) purge on the test chamber.

The results were then evaluated using the THERMAL ANALYST 2200 analysissoftware program, which identified and quantified the glass transitiontemperature of inflection, the endothermic and exothermic peaks, and theareas under the peaks on the DSC plots. The glass transition temperaturewas identified as the region on the plot-line where a distinct change inslope occurred, and the melting temperature was determined using anautomatic inflection calculation. The areas under the peaks on the DSCplots were determined in terms of joules per gram of sample (J/g). Forexample, the endothermic heat of melting of a resin or fiber sample wasdetermined by integrating the area of the endothermic peak. The areavalues were determined by converting the areas under the DSC plots (e.g.the area of the endotherm) into the units of joules per gram (J/g) usingcomputer software.

Example 1

A polylactic acid resin was initially obtained from Biomer, Inc. underthe designation BIOMER™ L-9000. A co-rotating, twin-screw extruder wasemployed (ZSK-30, diameter) that was manufactured by Werner andPfleiderer Corporation of Ramsey, N.J. The screw length was 1328millimeters. The extruder had 14 barrels, numbered consecutively 1-14from the feed hopper to the die. The first barrel (#1) received theBIOMER™ L-9000 resin via a volumetric feeder at a throughput of 40pounds per hour. The fifth barrel (#5) received varying percentages of areactant solution via a pressurized injector connected with an Eldexpump. The reactant solution contained 1,4-butanediol (87.5 wt. %),ethanol (6.25 wt. %), and titanium propoxide (6.25 wt. %). The screwspeed was 150 revolutions per minute (“rpm”). The die used to extrudethe resin had 4 die openings (6 millimeters in diameter) that wereseparated by 4 millimeters. Upon formation, the extruded resin wascooled on a fan-cooled conveyor belt and formed into pellets by a Conairpelletizer. Reactive extrusion parameters were monitored during thereactive extrusion process. The conditions are shown below in Table 1.This process produced hydorybutyl terminated PLA, which is chemicallydistinct from unmodified PLA.

TABLE 1 Process Conditions for Reactive Extrusion of Biomer L-9000 with1,4-Butanediol on the ZSK-30 Extruder Reactants Resin Titanium Extruderfeeding Butanediol Propoxide speed Extruder temperature profile (° C.)Torque Samples No. rate (lb/h) (%) (ppm) (rpm) T₁ T₂ T₃ T₄ T₅ T₆ T₇T_(melt) P_(melt) (%) PLA L-9000 40 0 0 150 188 190 190 184 194 176 140156 300  92-102 1 40 0.7 0 150 190 191 190 190 191 178 140 156 130 88-992 40 0.7 470 150 187 190 189 189 188 180 132 145 30 62-72 3 40 0.35 235150 190 188 190 191 189 178 130 142 70 79-86 4 40 1.2 820 150 189 191188 191 191 178 130 142 10 58-62

As indicated, the addition of 0.7 wt. % butanediol alone (Sample 1) didnot significantly decrease the torque of the control sample, althoughthe die pressure did drop somewhat. With the addition of 0.7 wt. %1,4-butanediol and 470 ppm titanium propoxide (Sample 2), the diepressure and torque decreased to a greater extent. The torque and diepressure could be proportionally adjusted with the change of reactantand catalyst.

Melt rheology tests were also performed with the control sample andSamples 1-4 on a Göettfert Rheograph 2003 (available from Göettfert inRock Hill, S.C.) at 180° C. and 190° C. with 30/1 (Length/Diameter)mm/mm die. The apparent melt viscosity was determined at apparent shearrates of 100, 200, 500, 1000, 2000 and 4000 s⁻¹. The results are shownin FIG. 2. As indicated, Samples 1-4 had lower apparent viscosities overthe entire range of shear rates than the control sample. The melt flowindex of the sample was determined by the method of ASTM D1239, with aTinius Olsen Extrusion Plastometer at 190° C. and 2.16 kg. Further, thesamples were subjected to molecular weight (MW) analysis by GPC withnarrow MW distribution polystyrenes as standards. The results are setforth below in Table 2.

TABLE 2 Apparent Viscosity (Pa · s, Melt Flow Average Mol. Wt. 1000 s⁻¹,Index (g/mol) Polydispersity Sample 190° C.) (g/10 min) M_(w) M_(n)(M_(w)/M_(n)) PLA L-9000 257 10.1 143500 109300 1.31 Control 252 10.7141900 107900 1.32 1 164 19.3 138900 105900 1.31 2 42 146 97200 705001.38 3 90 62.2 112900 83500 1.35 4 12 635.3 64900 41600 1.56

As indicated, the melt flow indices of the modified resins (Samples 1-4)were significantly greater than the control sample. In addition, theweight average molecular weight (M_(w)) and number average molecularweight (M_(n)) were decreased in a controlled fashion, which confirmedthat the increase in melt flow index was due to alcoholysis. Table 3,which is set forth below, also lists the data from DSC analysis of thecontrol sample and Samples 1-4.

TABLE 3 Glass transition Melting Peak Enthalpy of Sample temperature (°C.) temperature (° C.) melting (J/g) Control 62 170 37.9 1 60 169 39.4 258 165 38.6 3 59 168 36.5 4 54 162 38.0

As indicated, Samples 1-4 (modified with 1,4-butanediol) exhibited aslight decrease in their T_(g) and T_(m), which appeared to correlatewith higher catalyst concentrations.

Example 2

A modified resin of Example 1 (Sample 2) was used to form a meltblownweb (“MB”). Meltblown spinning was conducted with a pilot line thatincluded a Killion extruder (Verona, N.Y.); a 10-feet hose fromDekoron/Unitherm (Riviera Beach, Fla.); and a 14-inch meltblown die withan 11.5-inch spray and an orifice size of 0.015 inch. The modified resinwas fed via gravity into the extruder and then transferred into the hoseconnected with the meltblown die. Table 4 shows the process conditionsused during spinning.

TABLE 4 Modified PLA L-9000 MB spinning conditions Extruder ScrewPrimary Air Zone 1 Zone 2 Zone 3 Zone 4 Speed Torque Pressure Hose DieTemperature Pressure (F.) (F.) (F.) (F.) (rpm) (Amps) (Psi) (F.) (F.)(F.) (Psi) 385 375 375 375 4 4 72 375 380 400 34

A sample of the modified polylactic acid web was also collected andanalyzed with an electronic scanning microscope (“SEM”) at differentmagnitudes. A micrometer scale bar was imprinted on each photo to permitmeasurements and comparisons. FIGS. 3 and 4 show the images of the fiberweb at 100× and 500×, respectively. The web was then thermally bonded at80° C. for 30 seconds and again analyzed with an electronic scanningmicroscope. A micrometer scale bar is imprinted on each photo to permitmeasurements and comparisons. FIGS. 5-7 show the images at 100×, 500×,and 1000×, respectively.

While the invention has been described in detail with respect to thespecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

1. A method for forming a biodegradable polymer for use in fiberformation, the method comprising melt blending a first polylactic acidwith at least one alcohol so that the polylactic acid undergoes analcoholysis reaction, the alcoholysis reaction resulting in a second,modified polylactic acid having a melt flow index that is greater thanthe melt flow index of the first polylactic acid, determined at a loadof 2160 grams and temperature of 190° C. in accordance with ASTM TestMethod D1238-E.
 2. The method of claim 1, wherein the ratio of the meltflow index of the second polylactic acid to the melt flow index of thefirst polylactic acid is at least about 1.5.
 3. The method of claim 1,wherein the ratio of the melt flow index of the second polylactic acidto the melt flow index of the first polylactic acid is at least about10.
 4. The method of claim 1, wherein the ratio of the apparentviscosity of the first polylactic acid to the apparent viscosity of thesecond polylactic acid is at least about 1.1, determined at atemperature of 190° C. and a shear rate of 1000 sec⁻¹.
 5. The method ofclaim 1, wherein the ratio of the apparent viscosity of the firstpolylactic acid to the apparent viscosity of the second polylactic acidis at least about 2, determined at a temperature of 190° C. and a shearrate of 1000 sec⁻¹.
 6. The method of claim 1, wherein the secondpolylactic acid has a number average molecular weight of from about10,000 to about 105,000 grams per mole and a weight average molecularweight of from about 20,000 to about 140,000 grams per mole.
 7. Themethod of claim 1, wherein the second polylactic acid has a numberaverage molecular weight of from about 30,000 to about 90,000 grams permole and a weight average molecular weight of from about 50,000 to about100,000 grams per mole.
 8. The method of claim 1, wherein thepolydispersity index of the first and second polylactic acids is fromabout 1.1 to about 2.0.
 9. The method of claim 1, wherein the melt flowindex of the second polylactic acid is from about 10 to about 1000 gramsper 10 minutes.
 10. The method of claim 1, wherein the melt flow indexof the second polylactic acid is from about 100 to about 800 grams per10 minutes.
 11. The method of claim 1, wherein the second polylacticacid has an apparent viscosity of from about 5 to about 250Pascal-seconds, determined at a temperature of 190° C. and a shear rateof 1000 sec⁻¹.
 12. The method of claim 1, wherein the second polylacticacid has an apparent viscosity of from about 10 to about 100Pascal-seconds, determined at a temperature of 190° C. and a shear rateof 1000 sec⁻¹.
 13. The method of claim 1, wherein the second polylacticacid is terminated with an alkyl group, hydroxyalkyl group, or acombination thereof.
 14. The method of claim 13, wherein the secondpolylactic acid has the following general structure:

wherein, y is an integer greater than 1; and R₁ and R₂ are independentlyselected from hydrogen; hydroxyl groups; straight chain or branched,substituted or unsubstituted C₁-C₁₀ alkyl groups; and straight chain orbranched, substituted or unsubstituted C₁-C₁₀ hydroxalkyl groups. 15.The method of claim 1, wherein the first polylactic acid containsmonomer units derived from L-lactic acid, D-lactic acid, meso-lacticacid, or mixtures thereof.
 16. The method of claim 15, wherein the firstpolylactic acid is a copolymer that contains monomer units derived fromL-lactic acid and monomer units derived from D-lactic acid.
 17. Themethod of claim 1, wherein the alcohol is employed in an amount of fromabout 0.1 wt. % to about 20 wt. %, based on the weight of the firstpolylactic acid.
 18. The method of claim 1, wherein the alcohol isemployed in an amount of from about 0.5 wt. % to about 5 wt. %, based onthe weight of the first polylactic acid.
 19. The method of claim 1,wherein the alcohol is a monohydric alcohol.
 20. The method of claim 1,wherein the alcohol is a polyhydric alcohol.
 21. The method of claim 20,wherein the alcohol is a dihydric alcohol.
 22. The method of claim 1,wherein a catalyst is employed to facilitate the alcoholysis reaction.23. The method of claim 22, wherein the catalyst is a transition metalcatalyst based on a Group IVA metal, a Group IVB metal, or a combinationthereof.
 24. The method of claim 22, wherein the catalyst is employed inan amount of from about 50 to about 2000 parts per million of the firstpolylactic acid.
 25. The method of claim 1, wherein the alcoholysisreaction is conducted in the presence of a co-solvent.
 26. The method ofclaim 1, wherein melt blending occurs at a temperature of from about 60°C. to about 300° C. and an apparent shear rate of from about 100seconds⁻¹ to about 10,000 seconds⁻¹.
 27. The method of claim 1, whereinmelt blending occurs at a temperature of from about 150° C. to about220° C. and an apparent shear rate of from about 800 seconds-1 to about1200 seconds⁻¹.
 28. The method of claim 1, wherein melt blending occurswithin an extruder.
 29. The method of claim 1, wherein the secondpolylactic acid is extruded through a meltblowing die.
 30. A fibercomprising a biodegradable polylactic acid terminated with an alkylgroup, hydroxyalkyl group, or a combination thereof, wherein thepolylactic acid has a melt flow index of from about 10 to about 1000grams per 10 minutes, determined at a load of 2160 grams and temperatureof 190° C. in accordance with ASTM Test Method D1238-E.
 31. The fiber ofclaim 30, wherein the melt flow index of the polylactic acid is fromabout 100 to about 800 grams per 10 minutes.
 32. The fiber of claim 30,wherein the polylactic acid has an apparent viscosity of from about 5 toabout 250 Pascal-seconds, determined at a temperature of 190° C. and ashear rate of 1000 sec⁻¹.
 33. The fiber of claim 30, wherein thepolylactic acid has an apparent viscosity of from about 10 to about 100Pascal-seconds, determined at a temperature of 190° C. and a shear rateof 1000 sec⁻¹.
 34. The fiber of claim 30, wherein the polylactic acidhas a number average molecular weight of from about 10,000 to about105,000 grams per mole and a weight average molecular weight of fromabout 20,000 to about 140,000 grams per mole.
 35. The fiber of claim 30,wherein the polylactic acid has a number average molecular weight offrom about 30,000 to about 90,000 grams per mole and a weight averagemolecular weight of from about 50,000 to about 100,000 grams per mole.36. The fiber of claim 30, wherein the polylactic acid has the followinggeneral structure:

wherein, y is an integer greater than 1; and R₁ and R₂ are independentlyselected from hydrogen; hydroxyl groups; straight chain or branched,substituted or unsubstituted C₁-C₁₀ alkyl groups; and straight chain orbranched, substituted or unsubstituted C₁-C₁₀ hydroxalkyl groups. 37.The fiber of claim 30, wherein the first polylactic acid containsmonomer units derived from L-lactic acid, D-lactic acid, meso-lacticacid, or mixtures thereof.
 38. The fiber of claim 37, wherein the firstpolylactic acid is a copolymer that contains monomer units derived fromL-lactic acid and monomer units derived from D-lactic acid.
 39. Anonwoven web comprising the fiber of claim
 30. 40. The nonwoven web ofclaim 39, wherein the web is a meltblown web.
 41. A nonwoven laminatecomprising a spunbond layer and a meltblown layer, wherein the spunbondlayer, the meltblown layer, or both, are formed from the web of claim39.